As is known from U.S. Pat. No. 6,038,861 for example, gas turbines comprise a compressor for compressing air, a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor, and a turbine for expanding the hot gas produced by the combustor. Gas turbines are known to emit undesirable oxides of nitrogen (NOx) and carbon monoxide (CO). Two-stage combustion systems have been developed that simultaneously provide efficient combustion and reduced NOx emissions. In a two-stage combustion system of said kind, diffusion combustion is performed at the first stage for obtaining ignition and flame stability. Premixed combustion is performed at the second stage in order to reduce NOx emissions.
The first stage, referred to as the “pilot” stage, is normally implemented by means of a diffusion-type burner and causes significant increases in NOx emissions.
The main burner is arranged around the pilot burner. The main burner comprises a plurality of main fuel mixers, each having a swirler which generates turbulence in the airstream. Located in the center of the swirler is the fuel supply line which introduces the gas into the airstream.
FIG. 1 shows a fuel supply line with a heat shield in a main burner according to the prior art. The fuel supply line 16 is situated in the interior of a supporting structure 6 which is arranged in the center of the swirler 4. Fuel supply lines 16 which introduce the fuel from the interior of the supporting structure 6 into the swirler vanes 4 are located in the supporting structure 6. Upon exiting from the swirler vanes 4, the gas mixes with the compressed air.
Also situated in the interior of the supporting structure 6 is a holder 8 which conducts the fuel further to the tip 10 of the arrangement. Located inside the holder 8 is a heat shield 18 which insulates the fuel from the environment. Oil injection holes 19 are positioned at the end of the heat shield 18.
The heat shield 18 serves for thermally decoupling the supporting structure 6 of the swirler 4 from the oil ducts 16 in the interior of the arrangement. The heat shield consists of a tube which in the prior art was soldered or welded 12 into the supporting structure 6. The materially bonded connection points 12 prevent the deformation of the supporting structure 6 due to the colder heat shield 18, with the result that thermal stresses can be produced. Because of said potential stresses the maximally possible number of starts—and consequently also the maximum possible useful life—cannot be realized.